Usage:
3406, 3408, 3412 Engines In All Applications
- SUPPLEMENT: 04/23/84
SERVICE MAGAZINE, DECEMBER 20, 1982, PAGE 1. Put a mark through the article "Dimensions For Reconditioning Cylinder Blocks, Cylinder Heads" and make reference to an article with same title in this publication. This new article has new specifications and recommendations.
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During engine reconditioning, it is some times necessary to machine the cylinder block and/or cylinder head contact (mating) surfaces. Dealers have desired specifications for the amount of material that can be removed from these components.
The information which follows has the minimum block heights and the minimum head thickness to which the components can be machined. Also given are tolerances for valve projection, flatness and surface finish.
Cylinder Blocks
The minimum height for a 3406 Engine block is 425.02 mm (16.733"). The minimum height for 3408 and 3412 Engine blocks is 418.67 mm (16.483"). These dimensions are measured from the centerline of the crankshaft bore to the mating surface for the cylinder head as shown in Illustration 1.
Illustration 1. Measurement of block height.
The flatness across the whole contact surface of the block must be within 0.10 mm (.004") and within 0.05 mm (.002") for any 177 mm (7.0") section of the surface. The surface finish specification is 3.2 micrometers (125 microinches) maximum.
Cylinder Heads
The minimum thickness for the cylinder heads used on 3406, 3408 and 3412 Engines is 111.51 mm (4.390"). This dimension is measured from the top of the head to its mating surface as shown in Illustration 2.
The flatness across the whole cylinder head mating surface must be within 0.13 mm (.005"), within 0.025 mm (.001") for any 76.2 mm (3.00") section and within 0.013 mm (.0005") for any 6.35 mm (.250") section. The surface finish specification is 3.2 micrometers (125 microinches) maximum.
Illustration 2. Cylinder head nomenclature.
After the head has been machined, the projection of the valves must be checked with a depth gauge. The valve projection must be less than 0.20 mm (.008") to prevent contact betwen the valves and the pistons. See Illustration 3. If the valve projection is more than the specification permits, two methods can be used to shorten the projection. First, the faces of the valve seat inserts can be ground to decrease the projection. If, for any reason, this is not acceptable or if enough metal can not be removed from the insert, the insert must be removed and the counterbore must be machined. The counterbore must not be machined deeper than the amount of material machined from the head. For example, if 0.38 mm (.015") was machined from the cylinder head, a maximum of 0.38 mm (.015") can be removed from the counterbore. See Illustration 2.
Up to 0.38 mm (.015") of material can be machined from the top of the adapter seat to remove fretting. A minimum dimension of 16.89 mm (.665") between the top of the adapter seat and the bottom of the head is necessary after the seat has been machined. After the adapter seat has been machined, the 1.5 ± 0.5 mm × 45° (.06 ± .02" × 45°) chamfer at the top and bottom of the adapter threads must be machined again. See Illustration 2.
Illustration 3. Measurement of valve projection.